Condition: at room temperature.
In order to give an intuitionistic understanding about the droplets and
micro-structures of microemulsions in the SFME system, cryogenic
scanning electron microscopy (Cryo-SEM) was performed according to
previous reports,39, 40 and conducted on the above
microemulsion systems (points c, k and j in Figure 3) dissolving with or
without lignin from different subregions. It is clear to see the
existence of the discrete spherical droplets in the O/W microemulsion
system containing lignin (point c in Figure 3), where the average
diameter of the droplets is about 67 nm (Figure 5A and Figure S3A).
Figure 5B shows the micro-structure of B.C microemulsion (point k in
Figure 3) in presence of lignin. The obvious
sponge-like structures, which are
generated owing to the break of microemulsion droplets alongside the
interconnections between two phases,
are considered to be the feature
structure of B.C microemulsion. The Cryo-SEM image of W/O microemulsion
(point j in Figure 3) with lignin is also exhibited (Figure 5C) and the
average diameter of its droplets is around 50 nm (Figure S3B). These
Cryo-SEM images verify visually that the O/W, B.C and W/O microemulsions
are formed orderly with the increase of octane content
(WO) when the RP/W is fixed at 4.78.
Furthermore, the above O/W microemulsion without lignin was also
compared (Figure 5D). Surprisingly, the size of its droplets becomes to
the smallest one with an average diameter of 48 nm (Figure S3C).